1. Field of the Invention
The invention generally relates to integrated circuit technologies, and more particularly to phase change memory elements incorporated in integrated circuit memory devices.
2. Description of the Related Art
Phase change memory devices incorporate a material that undergoes a phase change under an external stimulus such as heat. The phase change is associated with a change in a physical or electrical property that can be measured to indicate the phase of the material. These phase change memory devices are comprised of cells of varying complexity arranged in various architectures such as crosspoint arrays. All phase change memory devices, regardless of layout and architecture, rely on measurement of the phase change to indicate memory storage. An example of phase change memory compatible with crosspoint architecture is taught in U.S. Pat. No. 6,579,760 (issued to Lung), the complete disclosure of which is herein incorporate by reference.
Phase change materials (PCM) come in many forms. For example, certain materials can be switched between two states of different electrical conductivity by changing their crystallographic state which can be achieved by heating the phase change material. A conventional approach is to detect the phase change through measurements of the resistance change that accompanies the phase change.
Switching may be accomplished by direct heating, as taught by U.S. Pat. No. 5,825,046 (issued to Czubatyj et al.) and U.S. Pat. No. 6,087,674 (issued to Ovshinsky et al.), the complete disclosures of which are herein incorporated by reference. This can be achieved by passing a high current through the PCM. Reading or sensing the state of the PCM is accomplished by passing a lower current also directly through the PCM. Moreover, direct switching requires large current densities in the PCM which subjects the PCM to significant stress. As such, the limited number of switching cycles may be a drawback of phase change memory devices, wherein the failure mechanisms are accelerated by the high current densities.
However, while the above-referenced U.S. patents and other conventional approaches disclose embodiments that were satisfactory for the purposes for which they were intended, there remains a need for a novel phase change memory architecture that eliminates the requirement of high currents to pass through the incorporated phase change materials.